A study of people exposed to Ground Zero has found that early responders and recovery workers at the site of the World Trade Center terrorist attack do not appear to have an increased risk of cancer overall so far. The workers were more likely to be diagnosed with certain types of cancer: prostate, thyroid, and multiple myeloma. However, the researchers caution that it’s not certain exposure to the site caused the increased risk.

Researchers from New York and Chicago analyzed data up through 2008 from the World Trade Center Health Registry, which contains health-related information about 21,850 rescue and recovery workers, and 33,928 people who lived, worked, or attended school in the area. Their findings were published December 19, 2012 in the Journal of the American Medical Association.

According to the report, rescue and recovery workers did not have a significantly increased risk of cancer overall when compared to the general population of New York State. However, the workers had a 43% higher risk of prostate cancer. They also had double the risk of thyroid cancer and almost triple the risk of multiple myeloma, a type of cancer formed by malignant plasma cells.

But these findings have some important limitations. For one, the increases were based on small numbers of cases, so it’s not clear how reliable these numbers are. Higher than average rates of cancer screening among the workers, especially for prostate and thyroid cancer, could account for some of the additional diagnoses. The researchers also did not have information on other cancer risk factors, such as family history or occupational exposures before or after September 11 that might have played a role for anyone who developed cancer.

Intensity of exposure to the site did not increase cancer risk. Those in the study who were not rescue or recovery workers did not have an increased risk of any specific cancer.

Experts caution this isn’t the last word on cancer risk from Ground Zero debris, as longer follow-up is needed.

American Cancer Society national vice president, intramural research, Elizabeth Ward, PhD, chairs the Science/Technical Advisory Committee for the Centers for Disease Control and Prevention's World Trade Center Health Program, created by Congress to provide medical services and compensation for first responders working at Ground Zero.

Ward said: "It is important to recognize that the relatively short time since the exposure limits what we can currently conclude from this type of data. A lack of evidence for increased cancer incidence does not rule out the possibility that increased risks will be observed in the future. In addition, the nature, intensity and duration of exposure varies widely among rescue and recovery workers and others in the registry, so lack of increases in the overall population does not rule out excesses in specific subgroups. Nonetheless, the study results are reassuring that there does not appear to be a large increase of cancer in WTC-exposed populations at this time."

The dust and smoke from the collapse of the twin towers contained asbestos, lead, and other cancer-causing materials. However, it’s not easy to prove a diagnosis of cancer came from exposure to the dust and smoke, and not from some other cause. Last year, medical researchers from New York City published a study showing that firefighters who responded to the attacks had about a 19% greater risk of developing cancer than firefighters who did not work at the site. But they were cautious about the results because they followed the firefighters for just 7 years after 9/11, and many types of cancer can take decades to develop.

Fifty-eight cancer types are on the list of covered illnesses for people who were exposed to toxins in the aftermath of the September 11 attacks. Researchers say longer follow-up of those exposed is needed, especially for types of cancer—such as lung cancer—that typically take a very long time to develop.

Citation: Association Between World Trade Center Exposure and Excess Cancer Risk. Published in the December 19, 2012 issue of the Journal of the American Medical Association (Vol. 308, No. 23). First author: Jiehui Li, MBBS, MSc, New York City Department of Health and Mental Hygiene, Long Island City, New York.